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XIII. On certain Sensory Organs in Insects, hitherto imclescribed* . 

 By J. Braxton Hicks, M.D. Lond., F.L.S. 



Read May 3rd, 1860*. 



BErORE proceeding to the details of the following communication, it will be weU to 

 remind this Society of the structures I have already pointed out as existing in the Insect 

 tribes, the consideration of which wiU serve to explain the nature of the new organs 

 about to be described. 



In a paper read before the Linnean Society on the 17th June, 1856 1, 1 called attention to 

 groups of hemispherical vesicles, disposed in rows, very regularly arranged, situated at the 

 base of the halteres in all Diptera. These vesicles are apparently formed of cuticle, beneath 

 which the ordinary chitine-layer is deficient, whereby a longer or shorter tube is formed, 

 according to the thickness of that layer at the part. I showed that the number of these 

 vesicles in some Diptera was great — sometimes as many as 360 on each halter. I also 

 pointed out that a very considerable nerve (the largest in the body except the optic) pro- 

 ceeded to the halter. I then, as also subsequently (Linn. Trans, vol. x x i i . p. 144), 

 showed that similar structures were to be found extending along the subcostal nervure 

 of the wings both of Diptera and of the 4-winged tribes ; more numerously in that of the 

 posterior wings and on the upper aspect. 



To these organs also nerves were clearly seen to pass from the thoracic ganglia. 



At the same time I showed that the elytra of the Coleoptera formed no exception 

 in conseqiience of their peculiar structure, but that the nerve, entering their base, 

 branched into numerous filaments, which ultimately terminated in vesicles pretty 

 uniformly scattered on the upper surface. 



At the time of reading that paper I had not found these organs on the under surface 

 of the elytron, but I now furnish a drawing of the under surface of that of Aroinia nios- 

 chata (Musk Beetle), in which the vesicles are distributed in the course of the nervure, 

 the nerve giving off branches to each vesicle (PL XVIII. fig. B). 



Although I had distinctly perceived the branches of the nerves passing to the vesicles 

 on the subcostal nervure of the wings and on the elytra, I had not, at the time of my first 

 notice of the subject, seen the nerves actually distributed to those more elaborate groups 

 on the base of the halteres. 



I now, however, am able to show this point most clearly in the halteres of (Estrus 

 Uqui (PL XVIII. fig. A). It will be seen that a branch passes directly to each of the 

 three principal groups at the base, while a small nerve only proceeds up to the head of 

 the organ. Thus it is proved that, whatever the function of these organs may be, the 

 largest nerve, except the optic, is distributed to them. 



Having pursued these investigations into the different members of insects, I beg now 



* It should be stated, that this paper was originally presented to the Royal Society, where it was read on the 26th 

 May, 1859 ; and an abstract of it was published in the Proceedings Roy. Soc, vol. x. p. 25. 

 t Journ. of Proceed. Linn. Soc, vol. i. p. 136. 



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